Gravel packing is a common completion method where a zone in a perforated cased hole is isolated after a screen assembly is put into place. A crossover tool allows the sand to be deposited on the outside of the screen with fluid returns coming back to the surface through the crossover tool. Many variations on the basic gravel packing technique are known and U.S. Pat. No. 4,253,522 is but one example.
More recently, the gravel packing of screens has been replaced, particularly in open hole, by a technique involving expanding slotted liners or screens. U.S. Pat. Nos. 5,366,012 and 6,263,966 are respectively illustrative of these two completion techniques. U.S. Pat. No. 3,482,629 illustrates a technique using patches that can be expanded to fill holes in screens.
Also known in the context of cased and perforated wellbores is the technique of isolating perforations between a pair of seals and chemically treating them with pumped fluids. Illustrative of this technique are U.S. Pat. Nos. 3,861,465 and 4,498,536. BJ Services offers a Roto Jet tool for placement of treating acid.
One issue in reliable screen operation is the mud cake on the wall of an uncased hole in which the screen is to be expanded. Expansion of the screen into the mud cake will adversely affect its subsequent performance and could lead to premature plugging. On the other hand, for certain operations in open hole, the presence of mud cake can reduce fluid losses into the formation. What is needed is a way to treat or clean up the open hole around the time when a screen assembly is being expanded or shortly thereafter. There is a disadvantage to a delay between removing the mud cake and expanding the screen as in the interim the dislodged cake can redeposit itself in the time it takes to jet or clean the uncased hole and when the screen is in place for expansion in a subsequent run.
Accordingly, one of the objectives of the present invention is to provide a method where the open hole is treated in advance of a screen expansion. Another objective is to treat the borehole wall and expand the screen assembly in a single trip. These and other advantages of the present invention will become more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below.